Both the types of COF can be expressed by the same equation as below (refer with the Fig.1):

μ= Ff/N………………Eq.1

Where,

Ff – Frictional force along the surface

N – Normal reaction perpendicular to the surface.

μ – Coefficient of friction between the block and the surface, for Static friction it is termed a μs and for kinetic or sliding friction it is termed as μs or μk .

Then what is the difference between static and kinetic friction coefficient?

For static COF the block must be in static or non-moving condition, i.e., you have to take the friction force value of the force which is applied to the block for giving motion to it but the force value has not yet reached to the limit that can move the block.

For sliding or kinetic friction coefficient, you have to consider the friction force value of the moving block.

Friction Coefficients table

Material-1

Material-2

Coefficient of static friction ( µs)

Coefficient of sliding friction ( µk)

Aluminium (Al)

Aluminium (Al)

0.42

0.34

Aluminium (Al)

Copper (Cu)

0.28

0.23

Aluminium (Al)

Steel

0.35

0.25

Aluminium (Al)

Titanium

0.34

0.29

Aluminium (Al)

PTFE

0.19

Aluminium (Al)

Teflon

0.19

0.18

Aluminium (Al)

Chromium (Cr)

0.27

0.22

Aluminium (Al)

Nickel (Ni)

0.33

0.25

Aluminium (Al)

Mild Steel

0.61

Aluminium (Al)

Glass

0.17

0.14

Aluminium (Al)

Graphite

0.16

Brake Material

Cast Iron (Fe)

0.40

Brass

Cast Iron (Fe)

0.3

Brass

Steel

0.35

0.24

Brass

Glass

0.2

Bronze

Titanium

0.36

0.27

Bronze

Ice

0.02

Bronze

Cast Iron (Fe)

0.22

Bronze

Steel

0.16

Cadmium (Cd)

Cadmium (Cd)

0.79

Cadmium (Cd)

Cast Iron (Fe)

0.52

Cadmium (Cd)

Mild Steel

0.46

Cobalt

Cobalt

0.56

Cobalt

Chromium (Cr)

0.41

Cobalt

Cast Iron (Fe)

0.41

Cobalt

Lead (Pb)

0.55

Chromium (Cr)

Chromium (Cr)

0.46

Chromium (Cr)

Cobalt

0.41

Chromium (Cr)

Cast Iron (Fe)

0.48

Chromium (Cr)

Nickel (Ni)

0.59

Chromium (Cr)

Lead (Pb)

0.53

Chromium (Cr)

Alumina

0.50

Chromium (Cr)

Zerconia

0.61

Chromium (Cr)

Teflon

0.09

0.08

Chromium (Cr)

Aluminium (Al)

0.27

0.22

Chromium (Cr)

Steel

0.25

0.21

Copper (Cu)

Copper (Cu)

0.55

Copper (Cu)

Cobalt

0.44

Copper (Cu)

Chromium (Cr)

0.46

Copper (Cu)

Cast Iron (Fe)

0.5

Copper (Cu)

Nickel (Ni)

0.49

Copper (Cu)

Zinc

0.56

Copper (Cu)

Aluminium (Al)

0.28

0.23

Copper (Cu)

Silver

0.48

Copper (Cu)

Steel

0.32

0.25

Copper (Cu)

Stainless Steel

0.23

0.21

Copper (Cu)

Teflon

0.13

0.11

Copper (Cu)

Zinc

0.56

Cast Iron (Fe)

Cast Iron (Fe)

0.51

Cast Iron (Fe)

Cobalt

0.41

Cast Iron (Fe)

Chromium (Cr)

0.48

Cast Iron (Fe)

Manganese (Mn)

0.51

Cast Iron (Fe)

Molybdenum (Mo)

0.46

Cast Iron (Fe)

Titanium

0.49

Cast Iron (Fe)

Zinc

0.55

Cast Iron (Fe)

Lead (Pb)

0.54

0.43

Cast Iron (Fe)

Steel

0.4

Cast Iron (Fe)

Tin (Sn)

0.55

0.32

Gold (Au)

Gold (Au)

0.49

Gold (Au)

Silver (Ag)

0.53

Gold (Au)

Lead (Pb)

0.61

Graphite

Graphite

0.18

0.14

Graphite

Aluminium (Al)

0.16

Graphite

Steel

0.18

Graphite

Glass

0.15

Glass

Aluminium (Al)

0.17

0.14

Glass

Steel

0.13

0.12

Glass

Teflon

0.1

0.1

Glass

Brass

0.19

Glass

Steel

0.13

0.12

Glass

Glass

0.9

Silver (Ag)

Silver (Ag)

0.5

Silver (Ag)

Gold (Au)

0.53

Silver (Ag)

Copper (Cu)

0.48

Silver (Ag)

Cast Iron (Fe)

0.49

Silver (Ag)

Lead (Pb)

0.73

Silver (Ag)

Alumina

0.37

Silver (Ag)

Zirconium

0.39

Steel

Steel

0.31

0.23

Steel

Titanium (Ti)

0.48

0.48

Steel

Nylon

0.35

Steel

Teflon

0.27

0.27

Steel

ABS

0.3

0.35

Steel

PVC

0.53

0.38

Steel

Chromium (Cr)

0.25

0.21

Steel

Glass

0.13

0.12

Steel

Graphite

0.18

Titanium Vanadium alloy (Ti-6Al-4V)

Titanium Vanadium alloy (Ti-6Al-4V)

0.36

0.3

Titanium Vanadium alloy (Ti-6Al-4V)

Bronze

0.36

0.27

Titanium Vanadium alloy (Ti-6Al-4V)

Steel

0.36

0.31

Titanium Vanadium alloy (Ti-6Al-4V)

Aluminium

0.41

0.38

Titanium Vanadium alloy (Ti-6Al-4V)

Chromium

0.38

0.33

Silicon Carbide (SiC)

Silicon Carbide (SiC)

0.52

Silicon Carbide (SiC)

Silicon Nitride (SiN)

0.53

Tungsten Carbide

Tungsten Carbide

0.22

Tungsten Carbide

Steel

0.45

Tungsten Carbide

Copper (Cu)

0.35

Tungsten Carbide

Cast Iron (Fe)

0.8

Teflon

Chromium

0.09

0.08

Teflon

Nickel

0.15

0.12

Teflon

Aluminium (Al)

0.19

0.18

Teflon

Glass

0.1

0.1

Teflon

Steel

0.18

0.16

Teflon

Titanium Vanadium alloy (Ti-6Al-4V)

0.23

0.21

Ice

Ice

0.01

0.01

Ice

Bronze

0.02

Leather

Metal

0.61

0.25

Leather

Wood

0.61

0.52

Wood

Wood

0.25

0.129

Wood

Brick

0.6

Wood

Metal

0.3

Wood

Concrete

0.61

Wood

Snow

0.14

Brick

Wood

0.6

Paper

Paper

0.28

Bitumen or Asphalt (Wet)

Rubber

0.25 – 0.75

Bitumen or Asphalt (dry)

Rubber

0.9

0.5 – 0.8

Concrete (Dry)

Rubber

0.6 – 0.85

Concrete (Wet)

Rubber

0.45 – 0.75

Although, reliable sources (mentioned at the reference section) has been used for compiling the above COF table but still the values shown are approximate only. The friction coefficient value changes not only with material but also with the position and orientation of the participating materials. So, if you need accurate COF value, you must obtain it by experiment only.Reference

ASM-VOL 18-FRICTION, LUBRICATION AND WEAR TECHNOLOGY

Friction Science and Technology FROM CONCEPTS to APPLICATIONS – By Peter J. Blau

Hi, I am Shibashis, a blogger by passion and engineer by profession. I have written most of the articles for mechGuru.com. For more than a decades i am closely associated with the engineering design/manufacturing simulation technologies. Disclaimer: I work for Altair. mechGuru.com is my personal blog. Although i have tried to put my neutral opinion while writing about different competitor's technologies, still i would like you to read the articles by keeping my background in mind.